Power Sharing Between Midspan and Endspan for Higher Power PoE

ABSTRACT

Methods and systems for higher power PoE are provided. Embodiments overcome system limitations to PSE power scaling by using an endspan-midspan configuration which allocates power to the PD from both an endspan PSE and a midspan PSE. Embodiments are particularly suitable for deployed PoE systems having limited power supplies and/or ports designed for lower power. Further, embodiments include power management schemes to enable the proposed endspan-midspan configuration to intelligently allocate power between the endspan PSE and the midspan PSE according to required PD power.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/898,152, filed Sep. 10, 2007, now allowed (Atty. Docket No.2875.1680001), which claims the benefit of U.S. Provisional PatentApplication No. 60/935,703, filed Aug. 27, 2007 (Atty. Docket No.2875.1680000), both of which are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to Power over Ethernet (PoE),and more particularly to higher power PoE.

2. Background Art

Ethernet communications provide high speed communications between dataterminals.

Power over Ethernet (PoE) systems enable power transmission over thesame transmission lines that carry data in an Ethernet link. Generally,power is generated at a Power Source Equipment (PSE) side of the PoEsystem and is carried over an Ethernet cable to a Powered Device (PD)side of the PoE system.

Today, enabling higher power PoE systems that comply with current IEEEPoE standards faces challenges. Particularly, system limitations existto supporting higher power supply in PoE systems. These limitations aremost problematic in the case of already deployed PoE systems, where asystem upgrade to increase power supply might be very difficult orrequire complete replacement of system equipment. This may be the case,for example, for existing PoE systems having limited power supplycapabilities and/or ports designed for lower power (e.g., chassis orstackable PoE systems).

There is a need therefore to overcome the above described systemlimitations to enable higher power PoE systems.

BRIEF SUMMARY OF THE INVENTION

Methods and systems for higher power PoE are provided herein.

Embodiments include PoE system configurations that enable concurrentusage of endspan and midspan powering in a PoE system. As such,embodiments can be designed to fully exploit the maximum powertransmission capacity of the Ethernet cable connecting the PSE to the PDin a PoE system.

Further, embodiments overcome system limitations to PSE power scaling byusing an endspan-midspan configuration which allocates power to the PDfrom both an endspan PSE and a midspan PSE.

Further still, embodiments include power management schemes to enablethe proposed endspan-midspan configuration to intelligently allocatepower between the endspan PSE and the midspan PSE according to requiredPD power.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 is a block diagram of a conventional Power over Ethernet (PoE)system.

FIG. 2 illustrates a more detailed illustration of a conventional powerPoE system.

FIG. 3 illustrates a conventional midspan configuration in a PoE system.

FIG. 4 illustrates a midspan configuration with a combination data andmanagement port.

FIG. 5 illustrates a PoE system using the Alternative A poweringtechnique.

FIG. 6 illustrates a PoE system using the Alternative B poweringtechnique.

FIG. 7 illustrates a PoE system using the Alternative B poweringtechnique in a midspan PSE configuration.

FIG. 8 illustrates an example PoE system using an endspan-midspanconfiguration according to an embodiment of the present invention.

FIG. 9 illustrates an example PoE system using an endspan-midspanconfiguration according to another embodiment of the present invention.

FIG. 10 illustrates an example PoE system using an endspan-midspanconfiguration according to another embodiment of the present invention.

FIG. 11 illustrates an example PoE system that uses a power managementchannel according to an embodiment of the present invention.

The present invention will be described with reference to theaccompanying drawings. Generally, the drawing in which an element firstappears is typically indicated by the leftmost digit(s) in thecorresponding reference number.

DETAILED DESCRIPTION OF EMBODIMENT(S) Overview

Today, enabling higher power PoE systems that comply with current IEEEPoE standards faces challenges. Particularly, system limitations existto supporting higher power supply in PoE systems. These limitations aremost problematic in the case of already deployed PoE systems, where asystem upgrade to increase power supply might be very difficult orrequire complete replacement of system equipment. Indeed, while it maybe easy to upgrade a chassis-based system's line card to support higherpower levels per port, it is very difficult to scale a system's powersupply to provide higher power as most chassis systems are alreadydeployed. This may be the case, for example, for existing PoE systemshaving limited power supply capabilities and/or ports designed for lowerpower (e.g., chassis or stackable PoE systems).

Accordingly, there is a need to overcome the above described systemlimitations to enable higher power PoE systems.

Embodiments of to the present invention include PoE systems and methodsto enable higher power PoE systems.

In one aspect, embodiments of the present invention include PoE systemconfigurations that enable concurrent usage of endspan and midspanpowering in a PoE system. As such, embodiments can be designed to fullyexploit the maximum power transmission capacity of the Ethernet cableconnecting the PSE side to the PD side.

In another aspect, embodiments of the present invention overcome theabove described PSE system limitations by using an endspan-midspanconfiguration which allocates power to the PD from both an endspan PSEand a midspan PSE. As such, the need for power supply scaling at the PSEis negated. In addition, the endspan-midspan configuration provides asuitable solution to scale the power of already deployed PoE systems.

Further, embodiments of the present invention include power managementschemes to enable the proposed endspan-midspan configuration tointelligently allocate power between the endspan PSE and the midspan PSEaccording to required PD power.

Introduction

FIG. 1 illustrates a high level diagram of a conventional Power overEthernet (PoE) system 100 that provides both DC power and datacommunications over a common data communications medium. Referring toFIG. 1, power source equipment 102 provides DC power over conductors104, 110 to a powered device (PD) 106 having a representative electricalload 108. The PSE 102 and PD 106 also include data transceivers thatoperate according to a known communications standard, such as the IEEEEthernet standard. More specifically, the PSE 102 includes a physicallayer device on the PSE side that transmits and receives high speed datawith a corresponding physical layer device in the PD 106, as will bediscussed further below. Accordingly, the power transfer between the PSE102 and the PD 106 occurs simultaneously with the exchange of high speeddata over the conductors 104, 110. In one example, the PSE 102 is a dataswitch having multiple ports that is communication with one or more PDdevices, such as Internet phones, or a wireless access point.

The conductor pairs 104 and 110 can carry high speed differential datacommunications. In one example, the conductor pairs 104 and 110 eachinclude one or more twisted wire pairs, or any other type of cable orcommunications media capable of carrying the data transmissions and DCpower transmissions between the PSE and PD. In Ethernet communications,the conductor pairs 104 and 110 can include multiple twisted pairs, forexample four twisted pairs for 10 Gigabit Ethernet. In 10/100 Ethernet,only two of the four pairs carry data communications, and the other twopairs of conductors are unused. Herein, conductor pairs may be referredto as Ethernet cables or communication links for ease of discussion.

FIG. 2 provides a more detailed circuit diagram of the PoE system 100,where PSE 102 provides DC power to PD 106 over conductor pairs 104 and110. PSE 102 includes a transceiver physical layer device (or PHY) 202having full duplex transmit and receive capability through differentialtransmit port 204 and differential receive port 206. (Herein,transceivers may be referred to as PHYs) A first transformer 208 coupleshigh speed data between the transmit port 204 and the first conductorpair 104. Likewise, a second transformer 212 couples high speed databetween the receive port 206 and the second conductor pair 110. Therespective transformers 208 and 212 pass the high speed data to and fromthe transceiver 202, but isolate any low frequency or DC voltage fromthe transceiver ports, which may be sensitive large voltage values.

The first transformer 208 includes primary and secondary windings, wherethe secondary winding (on the conductor side) includes a center tap 210.Likewise, the second transformer 212 includes primary and secondarywindings, where the secondary winding (on the conductor side) includes acenter tap 214. The DC voltage supply 216 generates an output voltagethat is applied across the respective center taps of the transformers208 and 210 on the conductor side of the transformers. The center tap210 is connected to a first output of a DC voltage supply 216, and thecenter tap 214 is connected to a second output of the DC voltage supply216. As such, the transformers 208 and 212 isolate the DC voltage fromthe DC supply 216 from the sensitive data ports 204, 206 of thetransceiver 202. An example DC output voltage is 48 volts, but othervoltages could be used depending on the voltage/power requirements ofthe PD 106.

The PSE 102 further includes a PSE controller 218 that controls the DCvoltage supply 216 based on the dynamic needs of the PD 106. Morespecifically, the PSE controller 218 measures the voltage, current, andtemperature of the outgoing and incoming DC supply lines so as tocharacterize the power requirements of the PD 106.

Further, the PSE controller 218 detects and validates a compatible PD,determines a power classification signature for the validated PD,supplies power to the PD, monitors the power, and reduces or removes thepower from the PD when the power is no longer requested or required.During detection, if the PSE finds the PD to be non-compatible, the PSEcan prevent the application of power to that PD device, protecting thePD from possible damage. IEEE has imposed standards on the detection,power classification, and monitoring of a PD by a PSE in the IEEE 802.3standard, which is incorporated herein by reference.

Still referring to FIG. 2, the contents and functionality of the PD 106will now be discussed. The PD 106 includes a transceiver physical layerdevice 219 having full duplex transmit and receive capability throughdifferential transmit port 236 and differential receive port 234. Athird transformer 220 couples high speed data between the firstconductor pair 104 and the receive port 234. Likewise, a fourthtransformer 224 couples high speed data between the transmit port 236and the second conductor pair 110. The respective transformers 220 and224 pass the high speed data to and from the transceiver 219, butisolate any low frequency or DC voltage from the sensitive transceiverdata ports.

The third transformer 220 includes primary and secondary windings, wherethe secondary winding (on the conductor side) includes a center tap 222.Likewise, the fourth transformer 224 includes primary and secondarywindings, where the secondary winding (on the conductor side) includes acenter tap 226. The center taps 222 and 226 supply the DC power carriedover conductors 104 and 106 to the representative load 108 of the PD106, where the load 108 represents the dynamic power draw needed tooperate PD 106. A DC-DC converter 230 may be optionally inserted beforethe load 108 to step down the voltage as necessary to meet the voltagerequirements of the PD 106. Further, multiple DC-DC converters 230 maybe arrayed in parallel to output multiple different voltages (3 volts, 5volts, 12 volts) to supply different loads 108 of the PD 106.

The PD 106 further includes a PD controller 228 that monitors thevoltage and current on the PD side of the PoE configuration. The PDcontroller 228 further provides the necessary impedance signatures onthe return conductor 110 during initialization, so that the PSEcontroller 218 will recognize the PD as a valid PoE device, and be ableto classify its power requirements.

During ideal operation, a direct current (I_(DC)) 238 flows from the DCpower supply 216 through the first center tap 210, and divides into afirst current (I₁) 240 and a second current (I₂) 242 that is carriedover conductor pair 104. The first current (I₁) 240 and the secondcurrent (I₂) 242 then recombine at the third center tap 222 to reformthe direct current (I_(DC)) 238 so as to power PD 106. On return, thedirect current (I_(DC)) 238 flows from PD 106 through the fourth centertap 226, and divides for transport over conductor pair 110. The returnDC current recombines at the second center tap 214, and returns to theDC power supply 216. As discussed above, data transmission between thePSE 102 and the PD 106 occurs simultaneously with the DC power supplydescribed above. Accordingly, a first communication signal 244 and/or asecond communication signal 246 are simultaneously differentiallycarried via the conductor pairs 104 and 110 between the PSE 102 and thePD 106. It is important to note that the communication signals 244 and246 are differential signals that ideally are not effected by the DCpower transfer.

Midspan PSE Configurations

As discussed above, in one example, the PSE 102 is a data switch thatthat is communicating data traffic with one or more PD devices, such asInternet phones, or a wireless access point. The data switch has aninput row of data ports and an output row of data ports, where any oneof the input data ports can to be switched to any one of the output dataports. Each data port typically includes a serial-to-parallel (i.e.SERDES) transceiver so that data can be received and transmitted using,high speed serial techniques, but are processed in parallel on chip.

Despite the advantages of PoE, many existing communications links do notutilize PoE. Accordingly, some existing switches are data-only switchesthat do not support power transfer, i.e., they are non-PoE switches.However, often these data-only switches may need to communicate with PDdevices on a small number of their ports. in this scenario, a midspanswitch is connected between the data-only switch and the PD devices soas to inject the DC power for the PD devices. This is known as a midspanPSE (the PSE is within a midspan switch) configuration, whereas anendspan PSE configuration (the PSE is within the data switch) is asdescribed above in FIG. 2.

FIG. 3 illustrates a conventional midspan communications system 300including a data-only switch 302, a midspan 306, multiple PD 314 a-m,and a midspan controller 320. The data-only switch 302 has multipletransceiver ports 304 a-n that are only capable of transmitting andreceiving data. In other words, the data-only switch 302 supports highspeed Ethernet communications, but does not support PoE and thereforecannot provide DC power to the PDs 314. (The data-only switch doessupport the communication of management traffic (e.g., packets), whichis just another form of data.) However, there are occasions (as shown inFIG. 3) where the data-only switch 302 communicates with Powered Devices314 a-m, which are designed to be powered over the communicationsmedium. Accordingly, the midspan 306 is inserted between the data-onlyswitch 302 and the PDs 314 so as to inject the DC power needed to supplythe PDs 314.

The midspan 306 includes transceiver data ports 308 a-m that communicatehigh-speed data with the data-only switch 302 over correspondingcommunications links 316 a-m. Likewise, the midspan 306 also includestransceiver data ports 312 a-m that communicate high-speed data with thePDs 314 a-m over corresponding communication links 318 a-m. The midspan306 includes a DC power supply 322 and magnetics (e.g. transformers)similar to that shown in FIG. 2, so as to inject the appropriate DCpower to supply the PDs 314 a-m. The conventional midspan 306 furtherincludes a management port 310 that is dedicated to passing powermanagement traffic between the data-only switch 302 and the midpsancontroller 320. The management traffic is necessary for the switch 302and the midspan controller 320 to communicate the power requirementneeds of the PDs 314, which are to be powered by the midspan 306. It isnoted that the management traffic may carry other management informationas well. For example, it could also carry manufacture's informationregarding the midspan. The midspan controller 320 then programs thepower supply 322 for each of the ports 312 a-m in the midspan 306 basedon the power requirement needs of the PDs 314 a-m. The midspancontroller 320 also performs various other house keeping functions forthe midspan 306 such as monitoring the power requirements of the variousports over time in comparison to the total power supply available.

The power management traffic is transmitted at a relatively low datarate compared to the high speed Ethernet data carried by the Ethernetlinks 316. Further, the midspan management port 310 is a dedicated portthat carries only management traffic, meaning the corresponding port 304n on the data-only switch 302 is also exclusively dedicated to carryingthe power management traffic. Given the relatively low data rate formanagement traffic, the conventional midspan configuration of utilizinga dedicated management port is an inefficient use of silicon chip areafor both the midspan 306 and the data-only switch 302. Further, thenumber of system ports, and therefore cost, is also increased by havinga dedicated management port. Still further, data switches preferablyhave an even number of ports, (e.g. 24, 48, etc.). Therefore the extramanagement port 304 n on the data switch adds an extra odd-numbered port(25 in FIG. 3) that detracts from the even symmetry of the silicondevice. A switch or midspan having an odd number of ports is inherentlyundesirable, due to the fact that most communication racks that housethe switches are typically designed to house devices with an even numberof ports.

it is noted that the management packets described herein include, butare not limited to, layer 2 or higher packets and frames of thewell-known IEEE communications layer protocol.

FIG. 4 illustrates a midspan communications system 400. Embodimentsaccording to midspan communication system 400 are described in detail incommonly owned U.S. patent application Ser. No. 11/518,942, filed Sep.12, 2006 (Attorney Docket No. 1875.9220001).

The midspan communications system 400 includes the data-only switch 302,a midspan 402, and the PD 314 a-m, where the midspan 402 is configuredsuch that it does not require a separate management port for theprocessing of power management traffic with the data switch 302.Accordingly, both the midspan 402 and the data-only switch 302 can beconfigured to more efficiently use their available silicon area.

The midspan 402 includes transceiver data ports 404 a-l that communicatehigh-speed data with the data-only switch 302 over correspondingcommunications links 408 a-l. Likewise, the midspan 402 also includestransceiver data ports 406 a-m that communicate high-speed data with thePDs 314 a-m over corresponding communication links 410 a-m. As withmidspan 306, the midspan 402 includes a DC power supply and magnetics(e.g. transformers) similar to that shown in FIG. 2, so as to inject theappropriate DC power to supply the PD 314 a-m.

The midspan 402 also includes a combination data and management port 412that processes both data and power management traffic. The powermanagement traffic is communicated between the data switch 302 and themidspan controller 320 so as to manage the DC power injection on theoutgoing midspan ports 406 a-m to the PDs 314 a-m. The data/managementport 412 processes both high speed Ethernet data from the data switch302 and the low speed power management traffic on the single port over acombined Ethernet and management link 414. The high speed Ethernettraffic is directed to any one of the ports 406 a-m so as to effectcommunication with the PDs 314 a-m. The low speed management traffic isdirected to the external midspan controller 320 so the data switch 302and the midspan controller 320 can communicate regarding the powersupply needs of the PDs 314. As such, the combination data andmanagement port 412 obviates the need for a dedicated management port onthe midspan 402, and on the data-only switch 302.

As seen in FIG. 4, this has an obvious benefit for the data-only switch302 because the port 304 n is freed-up for additional data-onlycommunications. Whereas, in the conventional midspan configuration 300,the switch port 304 n was needed for management traffic. Accordingly,the freed switch port 304 n can be used for an additional PoE data linkthat is coupled to another midspan, or it can be used for a non-PoE datalink. In other words, it can be used to communicate with non-PoEdevices. Alternatively, the freed switch port 304 n can simply beeliminated so that the data switch 302 has an even number of ports.Either way, the IC device area is more efficiently used as compared withthe conventional configuration that is shown in FIG. 3.

Power Over Ethernet (PoE) Powering Techniques

Current IEEE compliant PoE systems provide power using one of twopowering techniques. These powering techniques are known as “AlternativeA” and “Alternative B.”

FIG. 5 illustrates an IEEE compliant PoE system 500 using Alternative A.PoE system 500 includes an endspan 502 (also referred to as “endspan”)and a Powered End Station 506, connected by an Ethernet cable 504.

Endspan 502 is a data and power switch. Endspan 502 includes a PSE 508.Endspan 502 may also include other components similar to those describedabove with respect to PSE 102.

Powered End Station 506 includes a Powered Device (PD) 510. Powered EndStation 506 may also include other components similar to those describedabove with respect to PD 106.

Ethernet cable 504 includes four conductor pairs 512, 514, 516, and 518.Typically, Ethernet cable 504 is a CAT 5 cable. Alternatively, Ethernetcable 504 may be a CAT 3, CAT 5e, CAT 6, CAT 6a, or CAT 7, for example.

Endspan 502 transmits both data and power to Powered End Station 506. InPoE system 500, endspan 502 uses Alternative A to perform data and powertransmission. Accordingly, endspan 502 simultaneously applies data andpower onto the same two conductor pairs 512 and 518 of Ethernet cable504.

Conductor pairs 514 and 516 remain unused in PoE system 500. The endspancan alternatively use Alternative B to perform data and powertransmission, as illustrated in FIG. 6.

Similar to PoE system 500, PoE system 600 includes an endspan 602 and aPowered End Station 506, connected by an Ethernet cable 504.

Endspan 602 transmits both data and power to Powered End Station 506. Toperform that, however, endspan 602 uses Alternative B, which includestransmitting data and power on distinct conductor pairs of Ethernetcable 504. Accordingly, endspan 602 transmits power over conductor pairs514 and 516 and data over conductor pairs 512 and 518 of Ethernet cable504.

Alternative B can also be used when data is being provided from a dataswitch having no power transmission capabilities. This is shown in FIG.7, which illustrates a PoE system 700 using a midspan PSE configuration.

PoE system 700 includes a Non-PSE Data Switch 702, a Midspan PSE 704,and a Powered End Station 506.

Non-PSE Data Switch 702 is a data-only switch. Accordingly, Non-PSE DataSwitch 702 provides only data over conductor pairs 512 and 518 ofEthernet cable 504. Data carried by conductor pairs 512 and 518traverses Midspan PSE 704 without any modification to reach Powered EndStation 506, where it is received. As illustrated, conductor pairs 512and 518 are coupled directly to conductor pairs 712 and 714 of Ethernetcable 716, which connects Midspan PSE 704 and Powered End Station 506.

Midspan PSE 704 is used to compensate for the lack of power transmissioncapabilities of Non-PSE Data Switch 702. As such, Midspan PSE 704includes a PSE 706. Midspan PSE 704 can be placed anywhere along theEthernet path between Non-PSE Data Switch 702 and Powered End Station506. Midspan PSE 704 provides the DC power injection necessary to thepower the PD device(s) 510.

Combined Endspan-Midspan PoE Powering Techniques

As described above, embodiments of the present invention include PoEsystem configurations that enable concurrent use of endspans andmidspans. As such, midspans can be used to complement the power supplycapabilities of endspans, or vice versa. Embodiments of the presentinvention can be used to enable higher-power PoE systems. Further,embodiments of the present invention are particularly suitable forupgrading the power supply capabilities of deployed PoE systems. Forexample, PoE systems having limited power supply capabilities and/orports designed for lower power (e.g., chassis or stackable PoE systems)can benefit from embodiments of the present invention. This overcomessystem limitations, particularly PSE power scaling limitations, toenabling higher-power PoE systems.

FIG. 8 illustrates an example PoE system 800 that uses anendspan-midspan configuration according to an embodiment of the presentinvention.

PoE system 800 includes an endspan 502, a Midspan PSE 704, and a PoweredEnd Station 506.

As illustrated, both endspan 502 and Midspan PSE 704 include PSEs. Assuch, higher power can be generated to provide to PD 510 of Powered EndStation 506, overcoming the PSE power scaling limitation describedabove. This is because both endspan 502 and Midspan PSE 704 provide DCpower to Powered End Station 506, instead of just one PSE.

In example PoE system 800, endspan 502 uses the Alternative A poweringtechnique. As such, endspan 502 uses data pairs 512 and 518 of Ethernetcable 504 to transmit power to Powered End Station 506. As in midspanconfiguration 700, conductor pairs 512 and 518 traverse Midspan PSE 704without any modification, before they are coupled directly to conductorpairs 712 and 714 of Ethernet cable 716.

Midspan PSE 704 uses the Alternative B powering technique. As such,Midspan PSE 704 uses unused (i.e., carrying no data) conductor pairs 708and 710 of Ethernet cable 716 to transmit power to Powered End Station506. Note that conductor pairs 514 and 516 of Ethernet cable 504, whichconnects endspan 502 and Midspan PSE 704, are unused and terminate atMidspan PSE 704.

As illustrated in FIG. 8, the endspan-midspan configuration of examplePoE system 800 fully exploits the power transmission capacity of theEthernet path that powers the PD. In other words, PD 510 receives powerover all four conductor pairs of Ethernet cable 716. It is noted that,according to IEEE 802.3, a PD can receive power over any conductor pairof the Ethernet cable. Additional circuitry may be needed at PD 510 toenable PD 510 to receive power over all four conductor pairs of Ethernetcable 716.

FIG. 9 illustrates an example PoE system 900 using an endspan-midspanconfiguration according to another embodiment of the present invention,whereby the midspan PSE uses the Alternative A powering technique.

PoE system 900 includes an endspan 902, a Midspan PSE 904, and a PoweredEnd Station 506.

Endspan 902 is substantially similar in terms of components andfunctions to endspan 502, described above. However, endspan 902 uses theAlternative B powering technique. As illustrated, PSE 508 of endspan 902uses unused (i.e., carrying no data) conductor pairs 514 and 516 ofEthernet cable 504 to transmit power to Powered End Station 506 via themidspan 904. Conductor pairs 514 and 516 directly couple respectively toconductor pairs 910 and 912 of Ethernet cable 914, which connectsMidspan PSE 904 and Powered End Station 506.

On the other hand, Midspan PSE 904 uses the Alternative A poweringtechnique. As such, in addition to including a PSE 706, Midspan PSE 904includes transformer circuitry to apply power generated by PSE 706 ontodata conductor pairs 906 and 908 of Ethernet cable 914.

Similar to example PoE system 800, the endspan-midspan configuration ofexample system 900 fully exploits the power transmission capacity of theEthernet path that powers the PD. Indeed, PD 510 receives power over allfour conductor pairs of Ethernet cable 914. Further, the PSE powerscaling limitation described above is similarly eliminated by poweringPD 510 using both PSE 508 and PSE 706.

It is noted that a choice in favor of one or the other of the twoconfigurations of example systems 800 and 900 may depend on the powercapabilities of the endspan and the midspan, the positioning of themidspan relative to the powered end station, and/or the resistance ofthe Ethernet path (including the connectors) between the endspan and thepowered end station.

Higher data rate implementations of the endspan-midspan configurationaccording to the present invention are also possible. For example,configurations that support 1000BASE-T, 2.5GBASE-T, 5GBASE-T, and10GBASE-T can be implemented. FIG. 10 illustrates an example PoE system1000 that uses an endspan-midspan configuration according to anembodiment of the present invention and supports up to 1000BASE-T(Gigabit Ethernet) Ethernet communications.

Example PoE system 1000 includes an endspan 1002, a Midspan PSE 1004,and a Powered End Station 1006.

Endspan 1002 is substantially similar in terms of components andfunctions to endspan 502, described above. However, endspan 1002transmits data over all four conductor pairs 512, 514, 516, and 518 ofEthernet cable 504, which connects endspan 1002 to Midspan PSE 1004.Endspan 1002 also transmits DC power over conductors pairs 512 and 518,to provide a portion of the power for powered device 1008.

Conductor pairs 512 and 518 traverse Midspan PSE 1004 without anymodification, where they are directly coupled respectively to conductorpairs 1014 and 1016 of Ethernet cable 1018, which connects Midspan PSE1004 and Powered End Station 1006. On the other hand, power is injectedonto conductor pairs 514 and 516 at Midspan PSE 1004, before they arecoupled respectively to conductor pairs 1010 and 1012 of Ethernet cable1018.

At Powered End Station 1006, data is received on all four conductorpairs 1010, 1012, 1014, and 1016 of Ethernet cable 1018. Similarly,power is also received on all four conductor pairs 1010, 1012, 1014, and1016 to power PD 1008, greatly increasing the power available to powereddevice 1008.

As would be understood by a person skilled in the art based on theteachings herein, a variation of example PoE system 1000 would includeendspan 1002 transmitting power over conductor pairs 514 and 516 andMidspan PSE 1004 transmitting power over conductor pairs 512 and 518.

As such, example PoE system 1000 provides a high power, high data ratePoE system, which fully exploits both the total power and datatransmission capacity of the Ethernet path connecting the endspan to thePD. This allows PoE system 1000 to be used to power high-powered devicesnot supportable by current IEEE compliant PoE systems. Also, as withsystems 800 and 900, system limitations to enabling higher-power PoE areovercome. Particularly, limitations due to power scaling at the PSE canbe eliminated. This is especially beneficial for deployed PoE systemshaving limited power supply capabilities and/or ports designed for lowerpower (e.g., chassis or stackable PoE systems).

Power Management Scheme or for Endspan-Midspan Configurations

FIGS. 8-10, described above, illustrated different endspan-midspanconfigurations according to the present invention. As described, thedifferent configurations present efficient solutions for providingincreased power at the PD when the endspan PSE alone is not capable ofsupporting this increased power. These configurations include insertinga midspan PSE between the endspan PSE and the PD.

However, merely inserting a midspan PSE between the endspan PSE and thePD does not completely solve the problem. In fact, doing so would resultin undeterministic behavior, where any one of a number of scenarioscould occur. For example, one scenario that can be envisioned is thatupon connecting the PD to the PoE system, either the midspan PSE or theendspan PSE may discover the PD first, and, consequently, power itexclusively. Further, though it is unlikely that both the endspan PSEand the midspan PSE will simultaneously power the PD, were that to occurit may result in inefficient use of power. For example, each PSE mayattempt to independently power the PD without regard to the power beingprovided by the other PSE, resulting in the PD being eitherunder-powered or over-powered.

There is a need therefore to have the endspan PSE and the midspan PSEcooperate to jointly power the PD and to allocate supplied power betweenthem so as to make optimal use of available power. A power managementscheme according to the present invention, directed to enabling thisneeded endspan-midspan power cooperation, will now be described.

FIG. 11 illustrates an example PoE system 1110 which uses a powermanagement scheme according to an embodiment of the present invention.

PoE system 1100 uses an endspan-midspan configuration, as describedabove with respect to FIG. 9. Accordingly, PoE system 1100 includes anendspan 1102 and a Midspan PSE 1104, connected by Ethernet cable 504, asillustrated in FIG. 11. For ease of illustration, the PD being poweredby endspan 1102 and Midpsan PSE 1104 is not shown in FIG. 11.

Endspan 1102 includes a PSE 508 and a Host Controller 1106. HostController 1106 controls PSE 508 to supply a first output power overconductor pairs 514 and 516 of Ethernet cable 504. Similarly, MidspanPSE 1104 includes a PSE 706 and a Host Controller 1108. Host Controller1108 controls PSE 706 to inject a second output power over conductorpairs 512 and 518 of Ethernet cable 504.

Further, endspan 1102 and Midspan PSE 1104 respectively include ports1112 and 1114, which enable a power management channel 1110 betweenendspan 1102 and Midspan PSE 1104. In an embodiment, power managementchannel 1110 provides a communication channel between Host Controller1106 of endspan 1102 and Host Controller 1108 of Midspan PSE 1104.Accordingly, Host Controller 1106 is enabled, through Host Controller1108, to control PSE 706 of Midspan PSE 1104. Alternatively, HostController 1106 is enabled to directly control PSE 706 of Midspan PSE1104, without communicating with Host Controller 1108. As such, endspan1102 is enabled to configure both the first and the second output powerssupplied respectively by PSE 508 and PSE 706. In addition, as will befurther described below, this configuration of the first and secondoutput powers can be dynamically performed.

As shown in example PoE system 1100, ports 1112 and 1114 enable anout-of-band power management channel 1110, dedicated to power managementtraffic. This is similar to the communication of power managementtraffic in the PoE system of FIG. 3 described above. Alternatively, thepower management channel can be enabled over an existing in-band datachannel between endspan 1102 and Midspan PSE 1104. Accordingly, endspan1102 and Midspan PSE 1104 would each include a combinationdata/management port, as described above with respect to FIG. 4.

Communication between endspan 1102 and Midspan PSE 1104 can be achievedusing a Layer 1 (L1), Layer 2 (L2), or a Layer 3 (L3) protocol. Further,communication can be achieved via any one of serial communication,parallel communication, L2 packets, L3 packets, Link Layer DiscoverProtocol (LLDP) packets, Operation Administration and Maintenance (OAM)packets, and Ethernet packets.

According to an embodiment of the present invention, when a PD isconnected to PoE system 1100, each of endspan 1102 and Midspan PSE 1104independently performs detection and classification of the PD. Theclassification capabilities of endspan 1102 and Midspan PSE 1104 maydiffer depending on the communication protocols that endspan 1102 andMidspan PSE 1104 support to communicate with the PD. For example,endspan 1102 may be capable of communicating with the PD using a Layer 1(L1) or a Layer 2 (L2) protocol, where higher classification accuracy ofthe PD is achievable when the L2 protocol is used. Similarly, MidspanPSE 1104 may have capabilities to support L1 or L2 communication withthe PD. A baseline for classification using L1 and L2 can be found athttp://www.ieee802.org/3/at/public/nov06/diab_schindler_(—)1106_(—)1.pdf.

In an embodiment, endspan 1102 and Midspan PSE 1104 both use L2 inclassifying the PD. As such, PD classification is limited to a range ofpower levels. For example, in the case of IEEE 802.3at, the power rangeis limited to power levels of 15.4 Watts, 25 Watts, and 39 Watts.Accordingly, a PD that requires power in between these power levels willlikely receive higher power than it needs. Nonetheless, by givingendspan 1102 the ability to configure the first and second output powerssupplied from PSE 508 and PSE 706, overpowering inefficiency can bereduced. For example, one scenario that could occur when no powercoordination between endspan 1102 and Midspan PSE 1104 is used includesboth endspan 1102 and Midspan PSE 1104 each independently powering thePD, thereby providing the PD more than two times its required power.However, with endspan 1102 having the ability to configure the first andsecond output powers, endspan 1102 can have either PSE 508 or PSE 706,but not both, power the PD, thereby reducing by a half the overpoweringinefficiency. In other scenarios, endspan 1102 can have both PSE 508 andPSE 706 power the PD. Accordingly, endspan 1102 can configure the firstand second output powers from a fixed range of power levels according tothe required power of the PD.

In another embodiment, Midspan PSE 1104 uses L1 but endspan 1102 uses L2to classify the PD. As such, endspan 1102 can precisely determine thepower required by the PD. In an embodiment, Midspan PSE 1104independently specifies the second output power upon detection andclassification of the PD. For example, Midspan PSE 1104 specifies thesecond output power from a fixed range of power levels. Subsequently,however, endspan 1102 reconfigures the second output power after startup of the PD. In an embodiment, endspan 1102 dynamically configures thefirst and second output powers according to one or more of the powerrequired by the PD and available power at PSE 508 and PSE 706. Forexample, endspan 1102 may specify the first output power from a fixedrange of power levels and configure the second output power according tothe first output power and the required power of the PD. Alternatively,endspan 1102 may specify the second output power from a fixed range ofpower levels and configure the first output power according to thesecond output power and the required power of the PD. For example,assuming a PD requires 26 Watts, endspan 1102 may instruct PSE 706 (oralternatively PSE 508) to provide 15.4 Watts (from the fixed range ofpower levels enabled by L1 classification) and PSE 508 (or alternativelyPSE 706) to provide the remainder of 10.6 Watts. Accordingly, in thisscenario, PSE 706 provides very coarse tuning using a number of discretepower levels, and PSE 508 provides the incremental fine tuning toprovide substantially the exact power level desired by the PD.Alternatively, endspan 1102 may instruct one or the other of PSE 508 andPSE 706 to entirely provide 26 Watts. As such, the PD receives exactlythe amount of power it requires, resulting in optimal PD powerallocation. In another embodiment, endspan 1102 is an IEEE 802.3af powercapable endspan having L2 communication capability and the PD is ahigher power PD. As such, endspan 1102 can power the PD according to802.3af (i.e., supplying a maximum of 15.4 Watts) and instruct PSE 706to supply the remainder of required PD power.

It is noted that this optimal PD power allocation would not be possiblewithout power coordination between endspan 1102 and Midspan PSE 1104.Indeed, even if both endspan 1102 and Midspan PSE 1104 are capable of L2classification of the PD, sub-optimal PD power allocation can stilloccur if endspan 1102 and Midspan PSE 1104 independently attempt topower the PD.

Power sharing/coordination between endspan 1102 and Midspan PSE 1104 hasbeen described above with respect to a single PD being powered by thePoE system. However, as would be appreciated by a person skilled in theart based on the teachings herein, this can be extended to a PoE systemhaving a plurality of PDs, as illustrated in FIGS. 3 and 4, for example.

According to an embodiment of the present invention where multiple PINare being powered by the PoE system, Midspan PSE 1104 reports to endspan1102 the PDs that it discovers over its ports. For example, referring toFIG. 3. the PD may discover one or more PDs over its ports 312 a-m.Further, Midspan PSE 1104 may report to endspan 1102 its powercapability over each of its ports and its total available power.

Endspan 1102 may also discover one or more PDs over its ports. These PDsmay include PDs commonly discovered with Midspan PSE 1104 orindependently discovered by endspan 1102. Further, endspan 1102 hasinformation regarding its own power capability over its ports and itstotal available power.

Accordingly, endspan 1102 can determine how to optimally allocate powerbetween itself and Midspan PSE 1104 for each PD of the multiple PDsbeing powered by the PoE system. This optimal allocation takes intoaccount available power at endspan 1102 and Midspan PSE 1104, powersupply capabilities over the different ports of endspan 1102 and MidspanPSE 1104, and power requirements of the PDs.

Power allocation is generally performed at startup of the PoE system. Asdescribed above, however, power allocation can also be performeddynamically by endspan 1102 based on changes in available power atendspan 1102 and Midspan PSE 1104 and/or in power requirements of thePDs. For example, dynamic reconfiguration of power allocation may beperformed when a new PD is connected to the PoE system or when anexisting PD is disconnected from the PoE system.

Further features, according to the above, include the endspan 1102instructing Midspan PSE 1104 to supply or stop supplying power overcertain ones of its ports and/or to adjust power levels over otherports. Further, endspan 1102 may instruct Midspan PSE 1104 to powercertain PD ports when endspan 1102 can only provide legacy power levelsover these ports.

Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A Power over Ethernet (PoE) endspan, comprising: a first PSE thatsupplies a first output power over an Ethernet cable to a powered device(PD); a first host controller that controls the first PSE to configurethe first output power; and a port that couples the first hostcontroller, via a power management channel, to a second host controllerof a second PSE of a PoE midspan, coupled between the endspan PSE andthe PD, wherein the first host controller dynamically configures thefirst output power of the first PSE and a second output power of thesecond PSE according to one or more of a required power of the PD andavailable power at the first and second PSEs.
 2. The PoE endspan ofclaim 1, wherein the PoE endspan and PoE midspan respectively use theAlternative A and Alternative B powering techniques, as specified inIEEE 802.3, over the Ethernet cable.
 3. The PoE endspan of claim 1,wherein the PoE endspan and PoE midspan respectively use the AlternativeB and Alternative A powering techniques, as specified in IEEE 802.3,over the Ethernet cable.
 4. The PoE endspan of claim 1, wherein the PoEendspan and the PoE midspan independently detect and classify the PD. 5.The PoE endspan of claim 4, wherein the PoE midspan independentlyspecifies the second output power upon detection and classification ofthe PD.
 6. The PoE endspan of claim 5, wherein the PoE endspanreconfigures the second output power after start up of the PD.
 7. ThePoE endspan of claim 1, wherein the PoE endspan uses Layer 1 (L1)classification of the PD, thereby the first output power is specifiedfrom a fixed range of power levels according to a required power of thePD.
 8. The PoE endspan of claim 1, wherein the PoE endspan uses Layer 2(L2) power classification of the PD, thereby having the ability toprecisely determine a required power of the PD.
 9. The PoE system ofclaim 8, wherein the PoE endspan specifies the second output power froma fixed range of power levels and configures the first output poweraccording to the second output power and the required power of said PD.10. The PoE endspan of claim 8, wherein the PoE endspan specifies thefirst output power from a fixed range of power levels and configures thesecond output power according to the first output power and the requiredpower of the PD.
 11. The PoE system of claim 8, wherein the PoE midspanuses Layer 1 (L1) classification of the PD and specifies the secondoutput power from a fixed range of power levels, and wherein the PoEendspan re-configures the second output power according to the requiredpower of said PD.
 12. The PoE endspan of claim 1, wherein the powermanagement channel is an out-of-band channel dedicated to powermanagement traffic.
 13. The PoE endspan of claim 1, wherein the powermanagement channel is established over an in-band data channel.
 14. ThePoE endspan of claim 13, wherein the port is a data-managementcombination port.
 15. The PoE endspan of claim 1, wherein the first hostcontroller dynamically configures the first output power of the firstPSE and the second output power of the second PSE according to therequired power of the PD.
 16. The PoE endspan of claim 1, wherein thefirst host controller dynamically configures the first output power ofthe first PSE and the second output power of the second PSE according tothe available power at the first and second PSEs.
 17. A Power overEthernet (PoE) endspan, comprising: a first PSE coupled over an Ethernetcable to a powered device (PD); a first host controller that controlsthe first PSE; and a port that couples the first host controller, via apower management channel, to a second host controller of a second PSE ofa PoE midspan, coupled between the endspan PSE and the PD, wherein firsthost controller communicates with the second host controller to enablethe first PSE and second PSE to collectively provide respective firstand second output powers to the PD.
 18. The PoE endspan of claim 17,wherein the first host controller dynamically configures the first andsecond output powers according to one or more of a required power of thePD and available power at the first and second PSEs.
 19. The PoE endspanof claim 17, wherein the PoE midspan independently specifies the secondoutput power upon detection and classification of the PD.
 20. The PoEendspan of claim 19, wherein the PoE endspan reconfigures the secondoutput power after start up of the PD.